The present invention relates to a low permeation pinchoff connection and a method of bridging a low permeation barrier layer at a pinchoff end of a fluid tank for reducing permeation of gaseous fluids through the fluid tank.
Fluid tanks are common in several industries. For example, fuel tanks for motorized vehicles have been used for many years. Many of the current fuel tanks installed in motorized vehicles are made of plastic or metal. Plastic storage containers provide a number of advantages over those made of other materials. Some advantages include reduced weight, reduced cost for both materials and construction, and greater flexibility and shape. Along with these advantages, the ability of certain plastic containers to stretch or flex makes them useful in automotive applications. A problem in plastic tanks that manufacturers have experienced is fuel may permeate through the walls of the plastic tank. For example, monolayer polyethylene fuel tanks, while benefiting from the advantages mentioned above, suffer from a relatively high permeability to gasoline with respect to containers formed of other materials.
Several approaches have been taken to improve the permeability characteristics of plastic fuel containers or tanks. One solution to this problem has been a fuel tank formed of a multi-layer wall material that is composed of layers of polyethylene and an ethylene-vinyl alcohol copolymer (EVOH). The EVOH copolymer exhibits good gasoline vapor barrier properties.
Polyethylene-EVOH thermoplastics structures can be formed into a variety of container shapes using twin-sheet thermo-forming and blow molding techniques. Polyethylene-EVOH container walls typically have about five to seven layers. The five layers include polyethylene inner and outer layers and one EVOH layer with an adhesive layer on each side. Regardless of the forming process, there are areas on the fuel tank known as the pinchoff where opposing multilayer structures are xe2x80x9cpinchedxe2x80x9d together, e.g., to rejoin sheets in the case of thermoforming, or to rejoin parisons in the case of blow molding. This forms a continuous container. In a pinchoff region or area where the multilayer structures are brought together, typically two EVOH barrier layers from opposing walls are not able to re-bond to a continuous state. The resultant pinchoff area has a higher permeation rate than other portions of the container.
The present invention provides a low permeation pinchoff connection between first and second formed multilayer walls or sheets of a fluid tank for reducing permeation of gaseous fluids therefrom. The low permeation pinchoff connection seals a barrier layer of the fluid tank to reduce gaseous permeation therefrom. This is accomplished by bridging barrier ends of a low permeation barrier layer on a pinchoff end of a pinchoff region of the fluid tank. More specifically, a barrier bridge is disposed on the pinchoff end to bridge a pinchoff gap within which the barrier ends are separated. This provides continuity between the barrier ends and reduces gaseous permeation therethrough.